Global warming may be a boon for the ticks that transmit Lyme disease.

In the last few decades, the deer tick Ixodes scapularis has fanned out across the northeastern United States and southeastern Canada, with the bacteria that cause Lyme disease in tow. The first cluster of disease was recognized in Connecticut in the mid-1970s; health experts estimate that there are now around 300,000 cases of Lyme disease annually in the United States.

Climate change may be partly to blame for the disease’s rise and things could get worse in coming decades, say researchers led by Nicholas Ogden of the Public Health Agency of Canada in Saint-Hyacinthe, Quebec. Using climate simulations, the team showed that warm temperatures’ spread northward between 1971 and 2010 matched up with the ticks’ sprawl. Milder temperatures mean higher survival rates for larval ticks, the authors report March 14 in Environmental Health Perspectives.

Climate projections to 2070 suggest that ticks’ stomping grounds will continue to surge northward as previously chilly zones turn balmy and habitable. The study offers a taste of how climate change may drive future spread of Lyme and other infectious diseases, the authors say.